Lloyd Alter
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Windows Materials Basics
There are many different kinds of windows, that operate in different ways and serve different functions. But in the air conditioned era, people choose them for aesthetics rather than function, and the memory of what the different different windows do has been almost forgotten. In most single and multiple family dwellings now, there will be a lot of fixed glass and perhaps a tiny opening section of window; in apartments they are not even allowed to open more than four inches.
But it doesn't have to be this way; windows can be sophisticated tools for controlling ventilation in your home. But before we can look at the design of windows, we should look at what materials they are made from.
All varieties are available in different levels of complexity; some work in multiple ways. Look for ease of cleaning; old double-hungs need to be cleaned from the outside, new ones pop out for easy cleaning. Similarly, cheap casements just hinge and are hard to clean; good ones pivot out so that you can reach between the frame and the outside of the window to clean them.
Wood Windows
Why we like Wood Windows
Wood is a renewable resource, sequesters carbon for the life of its use, looks good and lasts a long time if properly maintained; Some windows in historic houses are hundreds of years old. It has good insulating value.
What we worry about
It isn't all sustainably harvested, and some are made of woods that come from rainforests where lumbering is causing deforestation. It requires more maintenance than other materials, although are available in vinyl or aluminum cladding to make them maintenance free.
Eco-factor of Wood Windows
If made from sustainably harvested timber, it is probably the greenest window you can get. See our information on FSC wood:
- Buying FSC Lumber is a Responsible Choice : Planet Green
- A Picture Is Worth: FSC vs SFI Forests : TreeHugger
Vinyl or PVC Windows
Why we like Vinyl and PVC Windows
It's cheap.
What we worry about
Where do we start. The production of vinyl uses fossil fuels and lots of chlorine. It probably has phthalates, an endocrine disruptor. If it burns, it produces dioxins and other toxic byproducts. It is not a h2 material and a double hung or slider window that is well-supported might last, but casements can sag. If they are any colour other than white or beige they can almost melt in the sun.
Eco-factor of Vinyl/PVC windows
Over at TreeHugger I have had a debate with another writer, John Laumer for five years about whether there is a role for vinyl windows. He and others say that their low cost makes them the only real choice for replacement of leaky old windows as a way of weatherizing and reducing energy waste. Some companies like Serious Materials are even calling their vinyl windows green, claiming that they can reduce energy consumption by 40 %.
But there are far more cost-effective ways of reducing energy loss than changing windows; in our Plane Green series "green your house for winter" we found that replacing windows, in terms of bang for your buck, was one of the worst things you can do. In older buildings the change can dramatically affect the historic character of the homes they are in. The window salesmen of today are much like aluminum siding salesmen of the fifties, Spend your Weatherization Money Wisely(watch tin men) promising huge savings that don't necessarily materialize. I suspect that huge portions of the weatherization grants and tax credits being offered by governments in North America are going to be blown on vinyl replacement windows, that could have been spent far more wisely on other things.
More on vinyl windows:
Look Out Any Window
A Year Ago in TreeHugger: A Defence of Vinyl
Vinyl Windows: John was Right and I was Wrong. I Think.
The Pluses and Minuses of Vinyl
Aluminum Windows
Why we like Aluminum Windows
Aluminum is one of the most recycled and most easily recyclable materials around, and 95% of it is. When well-designed, it works well, is fireproof and lasts forever, which is why it is the standard for high-rise residential buildings.
What we worry about
Being metal, it is a good conductor of heat, so design is important, to ensure that there is a good thermal break. It is expensive.
Eco-factor of Aluminum Windows
Usually made from recycled material and extremely durable.
Fiberglass Windows
Why we like Fiberglass Windows
Pultruded fiberglass is durable and a good insulator.
What we worry about
cost- more expensive than wood or vinyl.
Eco-factor of Fiberglass Windows
The most thermally effective windows on the market are pultruded fiberglass, getting R-values up to R12, better than a lot of walls. More: Serious Materials Makes Serious Windows
Glass in Windows
Almost all residential windows are double-glazed, and there are many options. Spacers used to be metal and conductive, so you would see condensation in the corners; now they are non-conductive. Glass can be tuned to the climate requirements, Low E to reflect heat for hotter parts of the country; Glass that transmits heat for northern parts of the country. Some have thicker glass for noise control near highways; some are even triple-glazed. Rare noble gases like argon or krypton are less conductive than air. The options are an essay on its own.
Storm Windows
Anyone wanting to increase the efficiency of their windows and considering replacement should consider storm windows as well, particularly in older houses with original windows. There are magnetic storm windows that snap on inside, and can save as much energy as replacing windows at a fraction of the cost. If you have a fixed budget to weatherize your home don't blow it all on the windows if storm windows are suitable and you have original windows in an older home.
Remember what the the National Trust for Historic Preservation says:
There is an epidemic spreading across the country. In the name of energy efficiency and environmental responsibility, replacement window manufacturers are convincing people to replace their historic wood windows. The result is the rapid erosion of a building's character, the waste of a historic resource, and a potential net loss in energy conservation. Typically replacement windows are vinyl, aluminum, or a composite with wood, and none will last as long as the original window. Repairing, rather than replacing, wood windows is most likely to be the "greener option" and a more sustainable building practice.
More on Green Windows
Planet Green Archives: Windows
How to Reclaim a Window
Low-Tech Tips: Tune Your Windows
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